1. Field of the Invention
The invention relates to an electrode structure for use in electric circuit interrupters of the type including a pair of separable electrodes disposed within a vacuumized chamber and, more particularly, to an electrode structure having at least one electrode comprised of an annular contact section and a slotted arc driving section surrounding the contact section for driving, circumferentially of the arc driving section, an arc column generated between the electrodes during circuit interruption.
2. Description of the Prior Art
First of all, a typical conventional vacuum-type circuit interrupter will be described with reference to FIG. 1 which is a longitudinal sectional view. The circuit interrupter comprises an evacuated envelope casing 10, cylinder flanges 11 and 12 secured to the opposite ends of the casing 10, upper and lower end caps 13 and 14 sealingly secured to the ends of the respective cylinder flanges 11 and 12, and an intermediate shield 15 secured to the casing 10. Located within the intermediate shield 15 are a pair of separable disc-shaped electrodes 20 and 30 having thereon annular contact sections 21 and 31, respectively. The lower electrode 20 is a movable electrode secured to a lower electrode rod 18 which extends through a bellows 16 and the lower end cap 14 and suitably mounted for vertical movement of the lower electrode contact section 21 into and out of engagement with the upper electrode contact section 31 without imparting the vacuum inside the envelop casing 10. The upper electrode 30 is a stationary electrode secured to an upper electrode rod 17 which extends through the upper end cap 13 and is sealingly secured thereto.
If the upper and lower electrodes 30 and 20 are in engagement with each other to close the circuit interrupter as shown in FIG. 1, a current I will flow through the annular contact sections 21 and 31. When the lower electrode 20 is moved away from the upper electrode 30 to open the circuit interrupter, an arc column will appear between the separated contact sections 21 and 31. In the presence of the interaction of a magnetic field produced by the arc column itself and a magnetic field produced by a circuit connected to the circuit interrupter, the arc column is very unstable and is driven along the surfaces of the electrodes in a radial direction outward to an outer peripheral region thereof under the influence of a magnetic field created by a current flowing through a ]-shaped path in the contact sections 21 and 31 to locally heat the region so as to cause a great amount of metallic vapors generated from the electrode surface. This will lower the degree of the vacuum inside the envelop casing 10 and spoil the circuit interrupting performance.
In order to effectively control the arc column appearing during circuit interruption so as to eliminate these disadvantages found in such conventional electrode structures, an attempt has been made to provide an arc driving section around at least one of the electrode contact sections, the arc driving section formed with a plurality of slots to divide it into arc driving segments for circumferentially driving the arc column without the arc column stopping on an outer peripheral region of the contact section so as to locally heat the region. This attempt is intended to enchance arc column cooling performance so that circuit interruption can occur at a current of zero.
Conventional electrode structures of this type having such an arc driving section are shown in FIGS. 2 to 5. FIGS. 2 and 3 are plan and side views showing a so-called spiral electrode structure which has an electrode 20 comprised of an annular contact section 21 and an arc driving section 24 formed with a plurality of curved slots 23 inwardly extending from its outer periphery to form arc driving segments 22 angularly spaced around the contact section 21 in a generally spiral configuration. In such a spiral electrode structure, however, the arc driving segments 22 have their side surfaces cut normally to the direction of circumferential movement of the arc column and thus it is difficult for the arc column moving along the surfaces of the arc driving segments 22 to shift across the slots 23 to the next arc driving segments 22. Therefore, the arc column will stop on the tip end regions of the arc driving segments 22 to locally heat the regions so as to generate metallic vapors from the electrode surfaces thereby reducing the degree of the vacuum inside the envelope casing 10 to spoil circuit interrupting performance.
FIGS. 4 and 5 are plan and side views showing a so-called -shaped electrode structure which has an electrode 20 comprised of an annular contact section 41 and an arc driving section 44 formed with four slots 43 inwardly extending from its outer periphery to form four arc driving segments 42 in a generally -shaped configuration. Since the arc driving segments 42 have their side surfaces cut normally to the direction of circumferential movement of the arc column, the -shaped electrode structure has the same disadvantages as described in connection with the spiral electrode structure of FIGS. 2 and 3.